The surface antigen, CD34 protein, is a member of a family of single-pass transmembrane sialomucin proteins with an apparent molecular weight (Mr) of approximately 115 kD. CD34+ cells are normally found in the bone marrow and umbilical cord blood, such as hematopoietic stem cells (HSCs), endothelial progenitor cells and activated endothelial cells of blood vessels. Current studies have pointed out that CD34+ hematopoietic progenitor cells are a well-characterized population of stem cells, which have been used clinically to reconstitute the hematopoietic system after irradiation or chemotherapy. Otherwise, in vitro studies have demonstrated that CD34 expressed on human vascular endothelial cells (HUVECs) show the angiogenic tip cell phenotype, as well as in vivo studies have illustrated that CD34−/− mice exhibit abnormal vessel morphology.
QBEND/10 is a mouse monoclonal antibody (mAb) raised against CD34 and confirmed its reactivity with the class II epitope of CD34. Due to most monoclonal antibodies originate from mouse, a human anti-mouse antibody (HAMA) or a human anti-chimeric antibody (HACA) might be evoked accordingly when the murine antibodies are applied in human therapy. Hence, the murine antibodies need to be humanized for clinical application to prevent this kind of adverse immune response.
Angiogenesis is the physiological process which related to the sprouting and growth of new vessels from an existing vasculature. Angiogenesis is also the most common pathway for neo-vessel growth in malignancy, and the process is thus called tumor angiogenesis.
Therefore, there is an urgent demand to develop a novel humanized monoclonal antibody against CD34 and a specific biological agents for inhibition of angiogenesis at present.